Servo mechanism



Dec. 12, 1950 N. L. COHEN 2,534,106

SERVO MECHANISM Filed March 2, 1946 2 Sheets-Sheet 1 FILTER {7 1 F AMP. :t F

TWO WIRE CIRCUIT a R MOD. FILTER AMF. 1 a? I7 I8 \9 91 'osc; 3 MOD. FILTER AMP 2\ 22. 23

INVENTOR.

NATHAN/EL L. COHEN (9M -Ta 64 Dec. 12, 1950 co N 2,534,106

SERVO MECHANISM Filed March 2, 1946 2 Sheets-Sheet 2 FILTER 050. f 28 21:3

m 1 33 I FILTER 42F MIXER AMP. 3 URCUIT CwPuNG 30 3 ..r\ 32 AMP 1 27 f a? 38 FILTER Z F MIXER AMP. 3E

FILTER M\XER AMP! 4| 4o ul 0 5 .1 ANGLE 0F 0 ROTOR 2.1. 7, 5 I 43 INVENTOR.

NATHAN/EL L. COHEN A TTORNE VS Patented Dec. 12, 1950 UNITED STATES PATENT OFFICE SERVO MECHANISM Nathaniel L. Cohen, Rockaway Beach, N. Y.

Application March 2, 1946, Serial N 0. 651,668

7 Claims. 1

My invention relates to a system for transmitting signals from a self-synchronous transmitter to one or more self-synchronous repeaters over less than the usual number of wires, and more particularly to a unique way I have discovered of accomplishing this desired result.

Attempts have been made in the past to transmit signals for the control of self-synchronous repeaters or similar devices over less than three conductors, One such scheme was proposed in which the angular position of the transmitter determined the output frequency of a variable frequency audio oscillator. This audio frequency signal was used to control the position of a repeater at the remote point.

The greatest disadvantage of this system is the fact that complete and continuous rotation of the repeater is not possible.

A second system which was described recently involved a series of ultra high frequency transmitters, with antenna systems arranged in spacetime angular displacement. The system involved a great deal of cumbersome equipment, and was workable ove only relatively short ranges.

I have discovered a means whereby .signals for the direct control of a self-synchronous repeater system over very great distances are readily transmitted over only two wires or by radio, permitting continuous control for all angles of rotation of the transmitter. My system utilizes a unique combination of carrier and sub-carrier signals to accomplish the desired result.

It is therefore an object of my invention to provide long distance remote control of a selfsynchronous repeater system.

It is a further object of my invention to provide a system for transmittin signals for the control of a self-synchronous repeater over a circuit having only two conductors.

Still another object of my invention is to provide continuous angular control of a self-synchronous repeater at remote locations.

These and other objects of my invention will become apparent from the following description and the accompanying drawings in which Figure 1 shows a standard self-synchronous repeater system utilizing a self-synchronous transmitter and a self-synchronous motor,

Figure 2 shows a block diagram of one part of my invention, namely, that portion connected to the self-synchronous transmitter.

Figure 3 shows a block diagram of another part of my invention, namely, that portion connected to the self-synchronous receiver or repeater.

Figure 4 shows a block diagram of the first part Y shown in Figure 1.

- 2 of my invention connected to a radio transmitting system.

Figure 5 shows a block diagram of the second part of my invention connected to a radio receiving system.

Figure 6 represents the voltage distribution as a function of rotor angle in a self-synchronous machine.

Throughout thi discussion, the term transmitter will indicate a self-synchronous transmitter or generator, a device for converting the angular motion or position of its rotor into a unique combination of electrical signals. In addition, the term repeater will indicate a selfsynchronous repeater, motor, control transformer or other self-synchronous machine, devices for converting electrical signals from a transmitter into angular motion or position of their rotors corresponding to the motion or position of the transmitter rotor The term repeater, unless otherwise qualified, is used generically to indicate a device which can either be a transmitter or self-synchronous motor or control transformer, as they are machines having electro-mechanical symmetry.

In order to describe m invention, I will review the general principles of operation of a selfsynchronous repeater system. The self-synchronous repeater is a machine similar to a wound rotor three-phase motor Or generator. It consists of a rotor, mounted with suitable bearings, having a coil of wire mounted thereon, and a stator havin three similar coils equally displaced about the axis of the rotor, so that the axis of an electric field induced therein is displaced 120 from the adjacent coil axes.

When coil 2 on the rotor of machine 5 is excited, the voltage in the various coils on the stator depends upon the angular position of the rotor. The variation of Voltage induced in each of the stator coils as a function of the position of the rotor is shown in Figure 6. It is to be noted that the combination of the three voltages and their slopes or derivatives is unique. That means that a repeater excited from the same source and connected to the first machine will have the same Voltages induced forthe same position of its rotor, and only for that position.

In operation as a torque transmission system, the transmitter and repeater are connected as In Figure l I have shown schematically a transmitter 5, comprising rotor 2 and stator coils 8, 9 and [0 of stator I; a repeater 6, comprising rotor 3 and stator coils of stator 4; alternating current power source I, and

are transmitted over. related voltages are used to modulate two sepa- Wires connecting both transmitter and repeater together and to the power source.

Assuming that rotors 2 and 3 are in the same angular position with respect to their own stators, when power source 'i is connected, voltages induced in coils S, 9 and it by the action of coil 2 will be identical with those induced in the corresponding coils of stator 4 due to the action of coil 3. Under these conditions, no current will flow in the stator windings, and hence no torque will develop tending to rotate either rotor.

If, however, coil 2 is now rotated through a small angle, it will have a different angular. position with respect to its stator I than coil 3 will have with respect to stator 4. Consequently, voltage differences will appear between the corresponding terminals of stator l and stator 4,an'd currents will flow. These currents will bein such a direction and of such a magnitude that a torque, due to the interaction of the rotor and stator fields, will be developed tending to turn rotor 3 Ito the same relative position as that of rotor 2. QS iinilarIy a torque will develop tending to turn rd'to'r "2 back to its original position, but it is assumed that themechanism which caused rotor 2 to turn originally resists this torque.

It is, or course, apparent that either 5 or B eaniactas the transmitter, and hence the system s Bilateral; i. e., either end will respond to action at the other. It may be observed that the voltage differences between the respective terminals of the tiwo stators is unique for each angular difference between the rotors, and hence no ambiguity of position can obtain. Although only the repeater is shown in Figure 1, any number of additional repeaters may be added to the system.

invention contemplates a unilateral arrangement whereby one self-synchronous mais designated the transmitter, and all other machines connected to the system act as repeaters having no returneffect on the transmitter. It

is possible, however, by using a multiple arrangement of the devices, to make the system bilateral. It is now apparent that the transmission of threerelat ed voltages from one machine, say the transmitter; to the other machine, the repeater, is essential to the operation of the system. It is also apparent that their relative magnitudes and phase must be maintained during transmission. The three voltages are naturally in phase at the transmitter, but it is clear that if transmitted ,over a long line, differences in the line might cause "a phase shift on one voltage and not the others. This would, of course, result in a distorted magneticfieldpattern in the machine with resultant inaccuracies.

I have discovered, however, a method'of 'preserving the relative amplitude and phase of a plurality'of voltages no matter what di'stan'ce'they I have found 'thatif two rats carrier waves of different frequency,'and if these carrier waves are transmitted over a line,

that the phase relation of the two'original voltages 'when'detected at the receiving end of the un ven be the same as at the sending end provided that the two carrier waves are synchronized, sothat'they will not be altered in'p'hase.

In particular I have found thatif one of the carrier waves is harmonically related to the other, then they will maintain the same renevegpnase provided that the higher frequency is synchronized fromthe'lower frequency. Ifiapply these principles ina'n'ovel way in myinv'ention.

In Figure 2 I have shown a transmitter 5 connected to a system of electrical transducers in which H, 16 and 20 are carrier oscillators of frequency f, 21 and 3], respectively; l2, II and 2| are identical mixers or modulators as, for example, ring modulators; I3, l8 and 22 are filters; 14, I9 and 23 are amplifiers, and I5 i an ordinary mixing amplifier which combines the signals from amplifiers l4, l9 and 23 and feeds into a two-wire line. 1,

' Power source I supplies a voltage of frequency F to coil 2 of the rotor. In addition, it supplies this same voltage to modulator I2. The voltage impressed on coil 2 induces, by transformer action, voltages'in coils '8, 8 and In. These voltages are in unique combination such that their sum around the loop consisting of coils 8, 9 and I0 is zero, the voltage induced in each coil being a function of the angular position of the rotor 2.

J The voltages induced in coils, anda-ppearing at terminals 91+? and -|0-8'-, are fed'to modulators I 1;and'2 1 respectively.

Oscillator ILSuDDIies a voltage of frequency f to modulator 12 which combines it'with the voltagefrom coil 2 to for'm'a modulated carrier wave of frequency -f. having two 'sidebands of frequency'f-FF and 'f-F, displaced from the carrier by the frequency of power source one being higher and One being lower in frequency, in addition to spurious frequencies.

Filter 93 accepts the carrier-and'principal sidebands, rejecting all spurious frequencies, and passes them to amplifier l4. Amplifier l4 amp1ifies the signal and feeds it to amplifier l5 which feedsit to the two wire line.

Similarly, :oscillator lfig'modulator 1'1, filter l8 and amplifier I9 accomplish the 'same fun'ctlon utilizing "as a modulating voltage that from 0011 10,-except that the carrier frequency is 2 and the "side'bands are of "frequency 2f+Fwand *2'f-"F. And in the same'manner the voltage from coil 8 is appliedas modulation to 't'heca'rrier 'froin'oscillator20, which has'afrequen'cyfif with sidebands of frequency Bf-FF and '3f- F, through the 'me- 'dium of modulator 2| ,filter 22 and'amplifie'r 23.

It is noted that ijnly two of "the three voltages developed ar undthe stator are utilized. This is sufficient for the third is necessarily equal to the 50 vcctdr 's'u'm of the other two. Hence, if these vditages aredetect'eid 'elsewh'ie'r'fe in thesyst'emfthe third vonageis synthesized by'v'etorially adding the two kriown'voltages.

'It is kno'wnby those skilledi-n the art that two voltages of different frequency whenappliedto "a carrier voltage as modulation rettiintheir same relativetime positidns inthemodulation'envelope. "similarly, "Ihavedis'covered that 't'wo cr morevcitages of the same'iir difierehtrrequene whn upso plied to a correspondin number of carrier waves F tain the "same "reassess-1b *as the hiotlulatii'ig a le ;Sinc e it assess-16a treat ses sysia' wmh figure z llatbfs l6 arrahgenient "where replace r the in with nausea multipliers Fe and 20' having output frequencies of 2; and 3f, respectively, and output voltages equal to that of oscillator H, and operated from oscillator II as the driving source. In all other respects the operation of my invention as embodied in this change is identical with that described above.

In Figure 4 I have shown the first part of my invention connected to a radio transmitting system. Numeral 24 represents all the elements described above and shown in Figure 2. Numeral 25 is a radio transmitter of any ordinary type such as AM, PM, FM or TM modulated by the output of 24; and 2e represents an antenna device of any ordinary type.

' terference between the various components there- In Figure 3 I have shown a two wire line connected to a coupling amplifier 2'! connected through filters 28, 36!, 3t and 39 to oscillator 25! and demodulators Si, 35, 3% and 4!, which are in turn connected to amplifiers 32, These amplifiers are connected to self-synchronous repeater through isolating transformers 33, 33 and 42. Oscillator 29 is connected to oscillators 35 and st providing a synchronizing signal to them.

Signals coming on the two wire line from amplifier l5 of Figure 2, located at the remote control point, are received and amplified by amplifier 2'! which feeds them to the filters. Filter 28 is an ordinary resonant filter circuit which passes only the fundamental carrier frequency f, rejecting all others. The output of this filter is supplied to oscillator 2!) as a synchronizing signal. Filter 38 is an ordinary band pass filter which passes the fundamental carrier frequency f and its principal sidebands f-i-F and f-F, rejecting all others.

These signals are fed from the output of 3G to demodulator or mixer 3!. Demodulator 3! in turn demodulates this signal, utilizing the signal of frequency from oscillator 29 as the necessary demodulating voltage. The output of 3! is then a voltage of the same frequency as the original power frequency F from power source i in Figure 2. is an ordinary amplifier, and fed through transformer 33, which serves to isolate the circuits of amplifier 32, to winding 3, the rotor of selfsynchronous repeater 6.

In a similar manner, filter 3s passes only the carrier frequency 2f and its principal sidebands ZfiF' to the demodulator 36 which, operating in conjunction with oscillator 35 of frequency 2 produces a voltage of frequency F which is amplified in amplifier 3'! and fed to one of the windings of the stator of repeater i5.

Tracing back through the circuit of Figure 2 reveals that this voltage is of the same frequency and proportional to the voltage developed in Winding H3 of the stator of transmitter ii. Similarly, filter 39, oscillator it and demodulator 4i cooperate to produce at the output of amplifier 40 a voltage proportional to the voltage of winding 8 of stator of transmitter 5. Since, as described previously, the phase relationships and relative magnitude of the voltages from the several windings of transmitter 5 were preserved on the several carrier signals, and since all of the demodulating signals from the local oscillators 29, 35 and 40 are synchronized, it follows that 3'! and 4d.

This is amplified in amplifier 32, which the output of each demodulator and hence the output of the corresponding amplifiers has the same relative phase and magnitude, one voltage with respect to the other, as the original signal from transmitter 5.

These voltages applied to the corresponding coils of repeater t will then cause the rotor of 6 to take up the same relative position as the rotor of transmitter 5. As mentioned in the above description, oscillator 2?: is synchronized from the incoming carrier signal from oscillator ll of Figure 2. This prevents hunting which would occur due to a general shifting in phase between the incoming carrier signals and the local oscillator signals. In a similar manner to that described in connection with frequency multipliers I6 and 2B of Figure 2, oscillators and may be replaced by the appropriate frequency multipliers, and oscillator 29 may be replaced by a tuned amplifier of frequency f.

In Figure 5 I have shown the second part of my invention connected to a radio receiving system in which 43 is an antenna system of any type, adjusted to receive signals transmitted by the system shown in Figure 4, and M is a radio receiving system connected to 43, and feeding 45 which represents all the elements embodied in Figure 3.

Therefore, I have shown means by which certain signals received on a two wire line or a radio system are utilized to operate a self-synchronous repeater, in correspondence with signals transmitted by a self-synchronous transmitter.

I have described my invention in terms of a self-synchronous torque transmission system. It is of course equally applicable to use with such devices as self-synchronous control transformers, differential self-synchronous motors, or other similar devices.

Since other applications of the principles embodied in my invention will be apparent to those skilled in the art, I prefer to have it .described by the following claims.

I claim:

1. In a signalling system, a self-synchronous transmitter comprising a rotor winding and a plurality of stator windings, a source of single phase electric power connected to said rotor winding, said stator windings being so positioned with respect to said rotor that in-phase voltages are induced therein of intensities unique for each relative angular position of said rotor winding with respect to each of said stator windings, a source of carrier current, means for modulating said carrier current by said single phase electric power, a self-synchronous receiver remotely disposed with respect to said transmitter, said receiver comprising a corresponding rotor winding and a corresponding plurality of stator windings, a single carrier transmission channel connecting said transmitter and receiver, means for transmitting said modulated carrier current over said channel and means at said receiver responsive to said modulated carrier current for energizing said stator winding of said receiver corresponding to the energization of said stator winding at said transmitter for effecting a, corresponding rotation thereof.

2. In a servo mechanism system, a self-synchronous transmitter comprising a rotor winding and a plurality of stator windings angularly disposed with respect to each other, :3, correspondingly constructed synchronous receiver, means for energizing said transmitter rotor from a source 'of alternating current, said stator windings having induced in each winding in-phase voltages of intensities corresponding to the angular position of the winding with respect to the rotor, means comprising a single carrier transmitting channel, a source of carrier currents, means for modulating said source of carrier currents by not more than one less than the total number of stator windings, means for transmitting said modulated carrier currents over said single transmitting channel, and means whereby the rotor of said receiver "is energized by signals of the same frequency as, andin phase with,-said source of alternating current for energizing said transmitter rotor and means lf'O'l energizing said receiver stator windings by said transmitted in-phase signal voltages of intensities corresponding to those in said transmitter :stator windings ior positioning said receiver rotor Windingsin a position corresponding to said transmitter winding.

3. In a servo system, -a self-synchronous rotary transmitter and receiver, means for energizing said transmitter from a source of alternating current, means including saidtransmitterfor-generating a plurality of voltages of intensities determined by the angular movement of said transmitter, a source of carrier currents, means .for modulating said source or" carrier currents in accordancewith the source of alternating current and in -accordance with the generated voltages, a single carrier transmission channel for transmitting said modulated signals to said ,zreceiver, means at said receiver for demodulating said signals to reproduce signals corresponding to said source of alternating current,-andto said iinduced voltages, means for energizing said receiver by said demodulated reproduced alternating current and induced voltages for operating said receiver to a position corresponding to said transmitter.

41. In a servo system, a rotatable transmitter and receiver, .means' for energizing said transmit-- ter from a source "of alternatingcurrent, means for generating a plurality of voltages of intensities dependent on the angular position of said transmitter, a plurality of sources of synchronized carrier currents, :means i or modulating one ot-said sources with said source alternatin current and for modulating said other sources "with individual cones of said generated voltages, 'a single carrier common transmission 3113111181 from said transmitter to said receiver :for 'all -.of said modulated signals, means at said receiver :for separating said pluralityof carrier-currents, means for demodulating said carrier currents :to reproduce signals corresponding to said alter-- hating current for energizingsaid receiver and to reproduce signals corresponding to said 1111- duced voltages to rotate said receiver :to a position corresponding to the rotatedtposition of said transmitter.

15. 'In a servo system, a transmitter and a ireceiver, a plurality 'of synchronized "carrier frequencies, means for energizing said transmitter 'froma source of alternating current, means for modulating :one of said carrier frequencies "with :said source of alternating current, a singlecarrientransmission channel between'saidtransmitter and receiver, means at said receiver for filtering out, demodulating and energizing said receiver by said demodulated signals corresponding to said source of alternating :current, :means for modulating other of said carrier frequencies by voltages of intensities in accordance with the angular position of said transmitter, means 'for transmitting said last mentioned signals lover said :channel, means at said receiver for filtering out each of said other carriers, demodulating said signals and energizing said receiver by said last mentioned demodulated signals "corresponding to said voltages to operate said receiver to a position corresponding to the angular rotation of said transmitter.

6. In a servo system, a movable transmitter and a movable receiver, a single transmission channel connecting said movable transmitter'and movable receiver, means at said transmitter for generating a lurality of in-phase voltages, each of an intensity associated with the angular position of said movable transmitter, means comprising a second plurality of synchronized voltages for simultaneously transmitting signals over said channel corresponding to not more thanlone less than said pluralityof variable intensity voltages and for transmitting over said channel said synchronizin voltages, and means at said receiver for segregating signals corresponding .tosaid plurality of voltagesandforoperating said receiver in accordance therewith to a position corresponding to the movement of said transmitter.

7. In a servo system comprising a movable transmitter and a movable receiver, asingleican rier circuit connection therebetween, means for energizing said transmitter irom a source of power, means for transmitting signals over said circuit corresponding to said source of power ifor energizing said receiver correspondingly, (means for generating in-phase voltages at said transmitter of intensities corresponding to the movement of said transmitter, means for transmitting signals corresponding to .said voltage intensities over said circuit, means for segregatingsaid signals from each other and said first mentioned signals at said receiver-and means for operating said receiver in accordance with said received signals correspondingto said voltage intensities at said transmitter for moving said receiver .in accordance with the movement of said transmitter.

NATHANIEL L. COHEN.

REFERENCES CITED The following references are of record in the :file of this patent:

UNITED STATES PATENTS Number Name Date 1,234,170 Johnson 'July.24,,19.1 7 1,576,195 Junken Mar. .9, 1926 1,941,615 Mirick Jan. 2, 1934 2,183,725 Seeley Dec. .19, 1939 2,256,482 Isbister et al Sept..23, .1941 2,256,487 Moseley et a1 Sept.23,11'94'1 2,462,117 Mikkelson et a1. Feb. 22, 19.49 

